fig11

Figure 11. Real-space nonlinear imaging and ultimate performance of exciton-mediated nonlinear responses in TMDs. (A) wavelength-dependent SHG images of triangular monolayer WSe₂ acquired under MPM, revealing spatially resolved modulation of SHG intensity as the excitation wavelength crosses different exciton-complex resonances; (B) TP-PL image of monolayer WS₂ excited at 1,060 nm, demonstrating direct real-space imaging enabled by exciton-mediated nonlinear absorption; (C) power-dependent integrated photoluminescence intensities of exciton complexes (exciton, trion, biexciton), confirming their distinct nonlinear excitation characteristics. (A-C) are adapted with permission^[29]. Copyright 2019, Optica Publishing Group; (D) schematic illustration of a plasmonic nanocavity-WS₂ hybrid system designed to enhance two-photon upconversion via exciton-plasmon coupling; (E) excitation power-dependent enhancement of upconverted emission intensity, demonstrating orders-of-magnitude amplification of exciton-mediated nonlinear response in the nanocavity; (F) representative plasmonic nanocavity structure shown as an inset image, highlighting the engineered electromagnetic confinement used to maximize nonlinear interaction; (G) time-resolved luminescence decay of WS₂ with and without nanocavity coupling, indicating modified exciton dynamics associated with enhanced nonlinear emission. Experimental results are shown by symbols. (D-G) are adapted with permission^[42]. Copyright 2025, Springer Nature. TP-PL: two-photon photoluminescence; PL: photoluminescence.